Car Care: Cooling System Maintenance
Make sure your cooling system is in tip-top shape.

For most drivers, a new car is their second biggest financial investment after a house, and they need it to run reliably for many years. The cooling system is one of the most important, yet often neglected regular maintenance items in any vehicle.

“Coolant (also known as antifreeze) prevents engine freeze-up in winter, reduces engine temperature in the summer, and protects the cooling system from rust and corrosion year round,” according to the AAA website.

Gasoline and diesel four-cylinder engines can produce up to 15,000 explosions per minute with flame temperatures topping 2,000 degrees Fahrenheit. The cooling system has to efficiently remove that heat energy to prevent damage to cylinder heads, blocks, pistons and gaskets. The engineers that create these engines carefully design the coolant flow passages to ensure that temperatures stay even at all times with no hot or cold spots.

Whether you experience brutal cold, blistering heat or both, coolant has to flow through those passages without freezing or boiling to work properly. Specially formulated antifreeze – typically based on a blend of ethylene or propylene glycol and water – can function over a temperature range of −34°F to +265°F. Other additives in the coolant help to inhibit corrosion of metal parts and lubricate the water pump.

Over time, coolant degrades due to the limited lifespan of the corrosion inhibitors and exposure to all that heat. Without the corrosion inhibitors, scale builds up and restricts flow in the cooling passages, heater core and radiator tubes. When this happens, leaks can develop, temperatures can climb and internal engine components, including the head gasket, can be damaged, leading to very expensive repairs.

A failed head gasket can easily cost thousands of dollars, and potentially much more while periodic cooling system flushes are cheap by comparison. The traditional glycol-based coolants used in many cars and trucks should be replaced according to the vehicle manufacturer’s recommendations, often about every two years or 30,000 miles. These coolants are easily identified by the fluorescent green or blue dye that is added to make it easier to identify leaks and spills. Many modern vehicles use newer, long life coolants that are designed to last five years or 150,000 miles. These coolants are usually orange or red, and should never be mixed with green coolants. Although the coolant itself lasts longer, these systems should still be checked and maintained regularly, according to the schedule in your owner’s manual.

The first step of cooling system maintenance is a pressure check. In order to raise the boiling point of the coolant above 250°F, all modern vehicles use pressurized systems. With the engine off and cold, a test device can pressurize the cooling system to check for leaks. The pressure ratings vary for different vehicles, but if the pressure holds steady at the recommended level, the system should be free of leaks. The pressure cap itself should also be tested to ensure that it holds and releases at the rated pressure. If it releases at too low a pressure, the coolant can boil while excessive pressure can cause hoses or gaskets to burst. Your dealer’s service department has the tools and the expertise to complete these tests quickly and accurately.

The rubber hoses that transfer coolant between the engine, radiator and heater core should also be inspected for cracks or bulges. The belt that drives the water pump and in some cases the fan should also be checked for cracks or stretching. Problematic hoses or belts should be replaced immediately. The front side of the radiator should also be carefully cleaned to remove the dead bugs and other road dirt that inevitably build up during driving. A thermostat in the system controls the flow of coolant between the engine and radiator and should be checked and replaced if it doesn’t open at the correct temperature.

The freezing and boiling points of the coolant can also be checked by testing the specific gravity. Using a special tool, coolant can be drawn out of the engine and tested. If the freezing point is too high, the coolant should be replaced.

The coolant is drained using a plug on the radiator, although some vehicles also have a secondary drain on the engine block as well. Drained coolant should always be properly disposed of and never dumped in a sewer or waterway. The sweet smelling glycol is attractive to many animals, but it is toxic. After draining, the system should be thoroughly flushed with water until it runs clear and free of the color of the coolant. The flushing should be done in the reverse of the usual flow direction to help to loosen and remove any scale or other contaminants that have built up.

After closing up all the drains, the system should be refilled with a 50/50 mixture of coolant and water. With the radiator pressure cap still off, the engine should be run with the fresh coolant for about 10 to 15 minutes to bleed any air out of the system. Air in the cooling passages will limit the pressure, which will lower the boiling point and potentially cause damaging hotspots in the engine. During this bleed procedure, the interior heating system should also be turned on high to ensure that air is forced out. Once it has been bled, the system should be topped off with coolant mixture, typically through the reserve tank, and the pressure cap should be reinstalled.

Besides having the specific tools, experience and knowledge necessary to maintain your vehicle properly, your dealership’s service department will collect used coolant and send it to a recycling facility for reprocessing. If you’re a do-it-yourselfer, service and parts personnel at your dealer can answer your questions and help you get the job done right.